Nature | Vol 582 | 25 June 2020 | 525
Article
Variable water input controls evolution of
the Lesser Antilles volcanic arc
George F. Cooper1,6 ✉, Colin G. Macpherson^2 , Jon D. Blundy^1 , Benjamin Maunder^3 ,
Robert W. Allen^3 , Saskia Goes^3 , Jenny S. Collier^3 , Lidong Bie^5 , Nicholas Harmon^4 ,
Stephen P. Hicks^3 , Alexander A. Iveson^2 , Julie Prytulak^2 , Andreas Rietbrock^5 ,
Catherine A. Rychert^4 , Jon P. Davidson^2 & the VoiLA team*
Oceanic lithosphere carries volatiles, notably water, into the mantle through
subduction at convergent plate boundaries. This subducted water exercises control
on the production of magma, earthquakes, formation of continental crust and
mineral resources. Identifying different potential fluid sources (sediments, crust and
mantle lithosphere) and tracing fluids from their release to the surface has proved
challenging^1. Atlantic subduction zones are a valuable endmember when studying
this deep water cycle because hydration in Atlantic lithosphere, produced by slow
spreading, is expected to be highly non-uniform^2. Here, as part of a multi-disciplinary
project in the Lesser Antilles volcanic arc^3 , we studied boron trace element and
isotopic fingerprints of melt inclusions. These reveal that serpentine—that is,
hydrated mantle rather than crust or sediments—is a dominant supplier of subducted
water to the central arc. This serpentine is most likely to reside in a set of major
fracture zones subducted beneath the central arc over approximately the past ten
million years. The current dehydration of these fracture zones coincides with
the current locations of the highest rates of earthquakes and prominent low shear
velocities, whereas the preceding history of dehydration is consistent with the
locations of higher volcanic productivity and thicker arc crust. These combined
geochemical and geophysical data indicate that the structure and hydration of the
subducted plate are directly connected to the evolution of the arc and its associated
seismic and volcanic hazards.
The 750-km-long Lesser Antilles volcanic arc (LAA), located along the
eastern margin of the Caribbean Plate, is the result of slow (1–2 cm per
year) westward subduction of Atlantic and proto-Caribbean oceanic
lithosphere (Fig. 1 ). Water hosted in hydrous phases within the subduct-
ing plate will be released as the slab sinks into the mantle and warms
up. As the water migrates out of the slab, the stress on faults is reduced,
causing earthquakes. At the same time, the addition of water to the
overlying mantle wedge reduces the solidus temperature, which may
enhance melting. LAA magma production rates lie at the lower end of
the global range, probably owing to the low convergence rates, and
are very unevenly distributed, being greatest in the centre of the arc
(Dominica and Guadeloupe)^4. The LAA also displays notable along-arc
variations in geochemistry, volcanic activity, crustal structure and seis-
micity^5 –^8. Subducting plate velocity and age are often held responsible
for variations in convergent margin behaviour^9 but are unlikely to have
first-order influence on lateral variations within the LAA as neither
vary greatly along-strike. Instead, variations in LAA magmatism and
seismicity have been proposed to reflect a combination of (1) a strong
north to south increase in sediment input^10 ; (2) subduction of bathym-
etric ridges below the central arc^11 , which may enhance plate stress and
coupling; and/or (3) subduction of strongly hydrated fracture zones^12
at several locations along arc (Fig. 1 ).
Current plate reconstructions^13 show the northern LAA to be under-
lain by ~90-Myr-old subducted lithosphere that formed at the equatorial
Mid-Atlantic Ridge and includes the Marathon and Mercurius fracture
zones (Fig. 1 ), whereas beneath the southern LAA, the subducted litho-
sphere is up to 120 Myr old and formed at the, now fully subducted,
proto-Caribbean mid-ocean ridge. The seafloor spreading rates were
slow in both cases. The boundary between the two seafloor-spreading
domains is clearly visible in both bathymetric and gravity data, pro-
jecting from the Demerara Plateau towards the central islands before
becoming obscured by the accretionary prism around Barbados (Fig. 1 ;
Extended Data Fig. 1).
Hydration of lithosphere formed by intermediate or fast spreading
occurs mainly in the mafic crust through faults that form as the plate
bends into the trench. By contrast, slow spreading produces highly
tectonized oceanic lithosphere with relatively thin mafic crust, pro-
nounced faults and sections of upper-mantle material exposed at
the seafloor^14. The transform faults at slow-spreading ridges, which
manifest as fracture zones in mature oceanic crust, are more seismically
https://doi.org/10.1038/s41586-020-2407-5
Received: 14 August 2019
Accepted: 26 March 2020
Published online: 24 June 2020
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(^1) School of Earth Sciences, University of Bristol, Bristol, UK. (^2) Department of Earth Sciences, Durham University, Durham, UK. (^3) Department of Earth Science and Engineering, Imperial College
London, London, UK.^4 University of Southampton, National Oceanography Centre, Southampton, UK.^5 Geophysical Institute (GPI), Karlsruhe Institute of Technology, Karlsruhe, Germany.
(^6) Present address: School of Earth and Ocean Sciences, Cardiff University, Cardiff, UK. *A list of authors and their affiliations appears at the end of the paper. ✉e-mail: [email protected]